In-frame triplet deletions in RHD alter the D antigen phenotype.

BACKGROUND: The deletion of three adjacent nucleotides in an exon may cause the lack of a single amino acid, while the protein sequence remains otherwise unchanged. Only one such in-frame deletion is known in the two RH genes, represented by the RHCE allele ceBP expressing a "very weak e antigen." STUDY DESIGN AND METHODS: Blood donor samples were recognized because of discrepant results of D phenotyping. Six samples came from Switzerland and one from Northern Germany. The molecular structures were determined by genomic DNA nucleotide sequencing of RHD. RESULTS: Two different variant D antigens were explained by RHD alleles harboring one in-frame triplet deletion each. Both single-amino-acid deletions led to partial D phenotypes with weak D antigen expression. Because of their D category V-like phenotypes, the RHD(Arg229del) allele was dubbed DVL-1 and the RHD(Lys235del) allele DVL-2. These in-frame triplet deletions are located in GAGAA or GAAGA repeats of the RHD exon 5. CONCLUSION: Partial D may be caused by a single-amino-acid deletion in RhD. The altered RhD protein segments in DVL types are adjacent to the extracellular loop 4, which constitutes one of the most immunogenic parts of the D antigen. These RhD protein segments are also altered in all DV, which may explain the similarity in phenotype. At the nucleotide level, the triplet deletions may have resulted from replication slippage. A total of nine amino acid positions in an Rhesus protein may be affected by this mechanism.

Presence of RHD in serologically D-, C/E+ individuals: a European multicenter study.

BACKGROUND: RHD blood group alleles with reduced or absent antigen expression are a clinically significant and heterogeneous group. STUDY DESIGN AND METHODS: To detail population genetics data on apparently D- individuals in central Europe, a six-center study was performed with participants from Austria, Germany, Slovenia, Switzerland, and Russia. A total of 1700 serologically D- samples, positive for C and/or E, were investigated. RESULTS: Observed unexpressed RHD alleles were 59 RHD-CE-D+ hybrid alleles, 9 apparently regular RHD, 1 new RHD(Y401X); DELs were 8 RHD(M295I), 6 RHD(IVS3+1G>A), and 1 new RHD(X418L); and weakly expressed RHDs were 2 weak D type 5, 1 weak D type 1, 1 RHD category VI type 1, and 1 novel weak D type 26. Although weak D type 26 was shown to have one of the lowest D antigen densities ever observed, it gave rise to anti-D immunization in a transfused D- individual. CONCLUSION: The relative occurrence of RHD among serologically D- samples, positive for C and/or E, differed significantly in the investigated central European regions. Considering the growing use of molecular typing techniques, correct identification of blood group alleles with scarce or missing antigen expression is of utmost clinical importance and requires reliable population-based frequency data.

DNB: a partial D with anti-D frequent in Central Europe.

To improve routine D typing and define transfusion strategy, it is important to establish the frequency of partial D alleles and their susceptibility to anti-D alloimmunization due to transfusion or pregnancy. We identified the partial D DNB that was caused by an RHD(G355S) allele associated with a CDe haplotype and whose phenotype presented a normal D in routine typing. The antigen density was about 6000 D antigens per red blood cell, and the Rhesus index was 0.02. Five anti-D immunization events with allo-anti-D titers up to 128 were observed. Twelve carriers of DNB were whites of Central Europe; the only Danish proband had Austrian ancestry. DNB was the most frequent partial D recognized so far in whites, occurring with frequencies of up to 1:292 in Switzerland. DNB was the underlying partial D phenotype in a relevant fraction of anti-D immunizations occurring in whites.

The DAU allele cluster of the RHD gene.

Variant D occurs frequently in Africans. However, considerably less RHD alleles have been described in this population compared with Europeans. We characterized 5 new RHD alleles, dubbed DAU-0 to DAU-4, that shared a T379M substitution and occurred in a cDe haplotype. DAU-1 to DAU-4 were detected in Africans with partial D phenotypes. They harbored one and 2 additional missense mutations, respectively, dispersed throughout the RhD protein. An anti-D immunization was found in DAU-3. DAU-0 carrying T379M only was detected by screening European blood donors and expressed a normal D phenotype. Within the phylogeny of the RHD alleles, DAU formed an independent allele cluster, separate from the DIVa, weak D type 4, and Eurasian D clusters. The characterization of the RH phylogeny provided a framework for future studies on RH alleles. The identification of the DAU alleles increased the number of known partial D alleles in Africans considerably. DAU alleles may be a major cause of antigen D variability and anti-D immunization in patients of African descent.

Novel alleles at the JK blood group locus explain the absence of the erythrocyte urea transporter in European families.

The Kidd (JK) blood group system is of importance in transfusion medicine. The Jk(null) phenotype is associated with absence of the urea transporter in erythrocytes and moderately reduced ability to concentrate urine. We and others recently reported different molecular alterations in the silenced Jkb-like alleles of Polynesians and Finns, populations with higher Jk(null) frequencies. Here we report novel molecular bases of this phenotype in Caucasians. Blood samples from a Swiss and an English family were investigated by serological methods, urea haemolysis test and JK genotyping. Genomic DNA and JK mRNA were sequenced. Genotyping showed homozygosity for Jka-like alleles. The Swiss Jk(null) alleles deviated from wild-type Jka sequence by a nonsense mutation in exon 7 causing an immediate stop codon (Tyr194stop). The English Jk(null) alleles revealed a genomic 1.6 kilobase pair deletion including exons 4 and 5, the former of which includes the translation start codon. Multiple mRNA splicing variants were detected in reticulocytes but exons 3-5 were absent in all transcripts analysed. Screening for these alleles was negative in random donors. Two novel molecular alterations at the JK locus were defined and a multiplex polymerase chain reaction method for detection of the five known silent Jk alleles was developed to complement JK genotyping in clinical transfusion medicine.